Such an arrangement for measuring radiation quanta is more particularly suitable for measuring X-ray radiation, in which event for measuring the energy of quanta the quanta are converted for detection into pulse signals. The arrangement is particularly suitable for measuring monochromatic radiation.
Such an arrangement for measuring radiation quanta is known from the book "Practical X-ray Spectrometry" by R. Jenkins and J. L. de Vries, Philips Technical Library, MacMillan 1970, In chapter 3 of this book, p. 47-67, the detection of X-ray radiation is described. Several detectors are described, inter alia detectors filled with rare gas, in which X-ray quanta ionize gas atoms and electrons released thereby ionize further gas atoms. Pulse signals occur as a detector output signal. A detection device for the detection of X-ray quanta is described in FIG. 3.2 of chapter 3 on page 52 of the hook. When the detector output signal is integrated inter alia via parasitic capacitances in the detection device described, integrated pulse signals are obtained, whose pulse height is a measure of the energy of the pulse signals. After integration the output signal of the detection device decreases comparatively slowly by discharge with a comparatively large time constant. In chapter 4, p. 68.89 of the book, the processing of the integrated pulse signals after pretreatment is described. For a so-called single channel, i.e. for monochromatic radiation, with X-ray radiation fluorescence spectrometry, a pulse discrimination device is described in FIG. 4.1 on page 68 of the book. The pulse discrimination device described selects integrated pulsatory signals, the pulse height of which lies between a minimum and a maximum value adjustable in the pulse discrimination device (a so-called "window"). It is assumed that the average height is proportional to the energy of the selected pulse signals for quanta having a given wavelength. A pulse height distribution is mainly obtained by the statistical properties of the detector due to quanta of a given wavelength incident upon the detector. The maximum value and the minimum value and the difference between the maximum and minimum values are different for each wavelength. Consequently, pulse signals of different wavelengths are to be distinguished. A disadvantage of the known arrangement is that with an increase in the number of pulses per unit time - an increasing number of quanta per unit time - , an increasingly larger number of pulse signals are lost. A dead time present in the arrangement for detecting and processing the quanta will play an increasingly larger part with an increasing number of pulse signals. If more than one pulse signal falls within the dead time only one pulse signal is distinguished. On page 53 of the book, a formula is given to correct afterwards for dead time a measured number of pulse signals determined from a pulse height distribution: EQU R.sub.c =R.sub.m /(1-R.sub.m .DELTA.),
where R.sub.m is the measured number of pulse signals, .DELTA. is the dead time of the arrangement and R.sub.c is the corrected number of pulse signals. It is assumed that the arrival of the pulse signals is susceptible to a statistical analysis. Further, the dead time .DELTA. depends, for example, upon the influence of temperature on various parts of the arrangement. As a result, - with very large numbers of pulse signals per unit time -; the corrected number of pulse signals R.sub.c is only a comparatively coarse approximation of the real number of pulse signals occurring during measurement. A further problem arising with an increasing number of quanta per unit time in the known arrangement is that the integrated pulse signals can be piled up in case quanta enter the detection device substantially simultaneously. In the known arrangement, piled-up integrated pulse signals ensuing therefrom will be seen in the "window" as one signal, as two signals, or will even not be seen at all therein depending upon the adjusted minimum and maximum values. Also this phenomenon, which gives rise to a deviation between the actual and the measured numbers of pulse signals, is a disadvantage of the known arrangement.